please help with Realistic STA-47

slateef

slateef

Active Member
Hello all,

The issue is that the left channel sounds very "tiny". The right is totally fine. The left's volume output is low and the bass and treble adjustments really don't do much. Any ideas where I should start to troubleshoot?

Also, there is a lamp going to the faceplate that reads "Overload". What does this mean? In what situation would this light be illuminated?

Thanks.
 
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How tiny is "tiny"? Can you hear the left channel while the right channel is playing? Or can you barely hear the left channel only when you swing the balance all the way over to the left and crank up the volume?
 
That receiver is a pretty simple 11w unit.

I assume your reference to "tiny" is actually "tinny" sounding low output on the left.
First, operate the speaker switch back and forth a few times to see if it clears up
Next, examine the circuit board that has the output transistors screwed to the metal heat sink (Small TO220 transistors either 2SD313 or 2SD789). See if any components looked burnt or are there any burn marks on the circuit board below any component. If you see this, there are problems with the power amp stage you will need to have addressed.
If not and everything looks OK, you can try replacing the small 3.3uf capacitor C401, as low volume and tinny sound can be caused by that capacitor opening.
But the overload light actually points to problems in the output stage.
 
rjd3000, I can hear the left while the right plays, it just sounds lower. The output from the left channel is just at a lower volume than the right channel. It also has MUCH lower bass output, regardless of volume or bass adjustment. It just sounds "tiny".

Tom B, the power switch back and forth had no effect, there does't appear to be any burn marks on the circuit board. I'll try to replace C401 and see if that solves the issue. Could the output transistor for the left side be bad (or would there be NO sound if that was the case)?
 
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Does anyone else agree that I should replace C401? Any other ideas? Are y'all sure that its not the output transistors?

Just want to be sure before I go and order a replacement for C401.
 
Your capacitor selection should work, even though it is non-polarized.

If the channel is "tinny" or "sharp" sounding with some distortion and no "punch" (very little bass) that can be a symptom of a failed output, especially in these lower-powered, less complex amplifiers. I've had a handful of Pioneer SX-450 and 550 units (15-20W) which exhibited the same symptoms caused by a failed output.

A little more diagnosis and a bit more information and detail could be helpful.

If you find the outputs have failed, KDS526Y and KSB596Y are equivalent replacements. However, failed outputs frequently cause associated damage, and items like the drivers and biasing resistors are often also damaged.

The unusual drivers can be replaced with KSC2316Y and KSA916Y devices. Everything else is fairly standard.
 
A Nichicon UFG or UES series should work nicely. The cap is directly in the audio path and these series are designed specifically for that application.
 
UPDATE:

I finally got around to it and replaced C-401 (and did C-402 while I was at it). No difference. The left speaker still has low volume and no bass (it sounds like it's all treble and adjusting the bass knob has no effect).

What should I do next? Replace the output transistors? They're Sanyo D313E, by the way.

Thanks.
 
Based on your comments, ideas, and lack of general troubleshooting, I think you're a little in over your head.
 
How rude.

I'm just an average Joe. Not an electrician or technician. Just asking for some help in how to go about troubleshooting and/or for someone to point me in the right direction. I've been on this board for a few months and have come across lots of very helpful, friendly people.

If you can't help, would it have been too much to ask for you to keep your comment to yourself?
 
I didn't mean to attack you - we all start somewhere and I get that but I was trying to make a point. Others and I can help - but you have to help us help you. And if you can't, well we won't get anywhere.
You suggested replacing the output transistors - test them first. Measure some voltages. Read up on this model or similar and study the schematic if you haven't already.

Advice has been given by very smart members in this thread, work off of it.
Tom B said check out the output stage - no follow up.
Watthour gave you transistor replacements and asked you for more analysis - no follow up.
If anything it's rude to ignore their questions as they are trying to help!
Let's get this thing fixed.
 
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